1. Field of the Invention
The present invention relates, in general, to semiconductor wafer cleaning apparatuses and, more particularly, to an improvement in such a wafer cleaning apparatus to clean several wafers at the same time while rotating the wafers held in a horizontal, laid-down position.
2. Description of the Prior Art
In order to clean and etch conventional small-sized semiconductor wafers having a diameter of not larger than 200 mm during a semiconductor producing process in the prior art, a plurality of wafers are primarily held in a vertically holding-type wafer cassette, which holds the wafers in a vertical, standing position. The vertically holding-type wafer cassette with the wafers is, thereafter, immersed in a wafer cleaning bath by a robot arm prior to performing a desired wafer cleaning and etching process in said bath.
However, in recent years, the semiconductor wafers trend to be enlarged in their diameters to 300mm or more, and horizontally holding-type wafer cassettes, designed to hold such large-sized wafers in a horizontal, laid-down position, have been proposed and used. Such horizontally holding-type wafer cassettes include two standardized types: front opening unified pod-type cassettes and open-type cassettes.
When a conventional wafer cleaning bath, originally designed to clean the 200 mm-diameter wafers, is used with the 300 mm-diameter wafers, it is necessary to use a wafer position changing device, which has a complex construction and is used for changing the position of the 300 mm-diameter wafers from a horizontal, laid-down position in the cassette to a vertical, standing position prior to immersing the wafers in the wafer cleaning bath. The use of such wafer position changing devices is inconvenient to users as follows.
That is, such a wafer position changing device, used for changing the position of the 300 mm-diameter wafers from the horizontal, laid-down position in the cassette to the vertical, standing position prior to immersing the wafers in the conventional wafer cleaning bath originally used with 200 mm-diameter wafers, undesirably enlarges the installation area required for the semiconductor producing system. In addition, the 300 mm-diameter wafers are inevitably exposed to the atmosphere for a predetermined period of time during such a wafer position changing process, and so the wafers are undesirably oxidized, and easily contaminated with impurities on their surfaces during such a wafer position changing process. The wafer position changing process also lengthens the processing time while immersing the wafers in the cleaning bath or taking the wafers out of the bath, thus deteriorating the productivity during a semiconductor producing process. Furthermore, the wafers are inevitably brought into contact with the wafer position changing device during the wafer position changing process, thus undesirably increasing the contamination of the wafer surfaces. Another problem experienced in the use of the wafer position changing device resides in that the device increases the equipment cost of the semiconductor producing system, and increases the production cost of semiconductor products.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a semiconductor wafer cleaning apparatus, which cleans a plurality of wafers at the same time in a wafer cleaning bath while rotating the wafers held in a horizontal, laid-down position, and preferably removes the conventional wafer position changing device from a semiconductor producing system.
In order to accomplish the above object, the present invention provides a semiconductor wafer cleaning apparatus, including a wafer feeding robot arm used for feeding wafers from a wafer cassette to a wafer boat and seating the wafers in the boat while maintaining a horizontal, laid-down position of the wafers. The wafer boat, with the horizontally laid-down wafers, is vertically moved downward by a boat drive unit to be immersed in a wafer cleaning liquid flowing in a wafer cleaning bath. Thereafter, the boat is rotated within the wafer cleaning liquid, and so the wafers are washed and cleaned by the wafer cleaning liquid while being maintained in the horizontal, laid-down position and being rotated horizontally. The apparatus does not requires the wafers to be changed in their positions from a horizontal, laid-down position to a vertical, standing position during a wafer cleaning process, and so the apparatus preferably removes the conventional wafer position changing device from a semiconductor producing system. This apparatus thus reduces the area for installing the system, and reduces the time the wafers are exposed to the atmosphere, and improves productivity while producing wafers.